SPECTRA AND STRUCTURE OF SILICON-COMPOUNDS .17. RAMAN AND INFRARED-SPECTRA AND VIBRATIONAL ASSIGNMENT FOR HEXAMETHYLDISILANE AND AB-INITIO CALCULATIONS FOR DISILANE AND HEXAMETHYLDISILANE

The IR spectra of gaseous and solid hexamethyldisilane between 4000 and 25 cm-1 and the far-IR spectrum of the liquids from 450 to 25 cm-1 have been recorded. The Raman spectra have been recorded from 3500 to 10 cm-1 for all three physical phases. Assisted by ab initio calculations, the vibrational spectrum of hexamethyldisilane has been assigned under D3d symmetry and the results of a normal coordinate analysis are discussed. No spectral features indicative of free internal rotation have been observed. Gradient ab initio calculations have been carried out for the disilane and hexamethyldisilane molecules using different types of basis sets. The structural parameters, rotational constants, unscaled and scaled frequencies and harmonic force constants have been reported for both disilane and hexamethyldisilane.